1. Field of the Invention
The present invention relates to an ink jet printing method and a mist-reduction-condition setting apparatus. More particularly, the present invention relates to a setting of conditions for maintaining high image quality while reducing mist caused by ink jet printing.
2. Description of the Related Art
Along with the proliferation of ink jet printing apparatuses, image quality and handling equivalent to those in silver-halide photography have been increasingly demanded. In a case where an image outputted by a conventional color ink jet printing apparatus is compared with the silver-halide photography, granularity in an image has long been seen as a problem in particular. The granularity is defined as an impression similar to a sense of roughness perceived when ink droplets printed on a print medium are visually recognized as dots. In order to reduce the granularity, provided recently is an apparatus which performs printing by using light color ink having lowered colorant concentration, in addition to basic four colors of cyan (C), magenta (M), yellow (Y) and black (K). Examples of the light color ink are light cyan (LC), light magenta (LM), light yellow (LY), light black (LK) and the like. Furthermore, also provided is an ink jet printing apparatus which is prepared in advance to handle so-called secondary color ink (particular color ink), such as red (R), green (G) and blue (B), in order to express a wide color gamut equivalent to that of the silver-halide photography.
Another reason why the granularity degrades the image quality is a low spatial frequency of dots arranged in a highlight region. To reduce the granularity, it is also effective to increase the spatial frequency, that is, to reduce a dot size, and to increase the number of dots.
For the above reason, recently, many ink jet printing apparatuses which uses the light color or particular color ink in conjunction with basic four color inks, and uses a print head which ejects small ink droplets of 2 pl or less, have been provided for achieving the quality equivalent to silver-halide photography.
In addition, the ink jet printing apparatus for achieving an outputted image equivalent to that of the silver-halide photography, also needs to be able to perform printing on the entire surface of the print medium (margin-less printing). In a case where the margin-less printing is performed by the ink jet printing apparatus, a significant problem is that a printed object and the inside of the apparatus are contaminated with ink ejected outside edges of the print medium at the time of printing. Japanese Patent Laid-Open No. 2000-351205 discloses an ink jet printing apparatus and an ink jet printing method contrived so as not to contaminate a print medium with ink ejected outside the print medium.
FIG. 1 is a view for explaining the ink jet printing method described in Japanese Patent Laid-Open No. 2000-351205. In FIG. 1, reference numeral 201 denotes a print head which is, here, in a state of carrying out printing in a front end portion of a print medium 207. The print medium 207 is fed and conveyed on a platen 206 which supports the print medium 207 from below, while being held with a pair of rollers which are a conveyance roller 202 and an auxiliary roller 203. Moreover, a front end of the print medium 207 is set in a position where printing can be performed by the print head 201. In the configuration disclosed in Japanese Patent Laid-Open No. 2000-351205, a hole H is provided to the platen 206, and an absorber for absorbing ink is further provided to the inside of the hole.
FIG. 2 is an enlarged view for specifically explaining a printing part shown in FIG. 1. As shown in FIG. 2, ink ejected outside the print medium 207 is absorbed by an absorber 209 disposed inside the hole H. As described above, by collecting, at a predetermined spot, the ink not applied onto the print medium, the print medium and the inside of the apparatus can be prevented from being contaminated, even though they might otherwise be contaminated due to scattering of the ink. With reference to FIG. 2, the explanation has been provided for the example of printing in the front end portion of the print medium. Meanwhile, the same explanation can be provided for printing in a rear end portion and in right and left end portions.
The position of the front end of the print medium is usually detected in the ink jet printing apparatus. Thus, margin-less printing can be performed without intentionally ejecting the ink to a region outside the print medium. However, a slight error inevitably occurs in terms of a degree of accuracy in conveying the print medium or in an ejection direction. For this reason, in order to achieve stable margin-less printing, it is desirable that the ink be ejected, to some extent, to the region outside the print medium. Note that an amount of ink ejected outside the print medium can be suppressed to be smaller than an amount of ink ejected onto the print medium. Japanese Patent Laid-Open No. 2002-086701 discloses a method for controlling an amount of ink applied near an edge of a print medium by processing image data, reducing energy for ejection or using a mask pattern to be described later, in margin-less printing.
However, the recent trends of using smaller ink droplets, margin-less printing, and an increase of colors of used ink have accelerated generation and scattering of mist inside the ink jet printing apparatus. The mist in the ink jet printing apparatus will be described below.
In the present specification, the mist is defined as minute ink droplets scattering inside the apparatus, unlike ink droplets ejected toward the print medium from the print head. Although the mist is generated in various circumstances, the mist is especially likely to be generated when the margin-less printing is performed, for example. This is because ink droplets ejected to the absorber positioned farther than the print medium is influenced by an airflow, air resistance and the like in a movement path of it, and then kinetic energy of ink droplet in a direction toward the absorber is likely to be lost.
It has been confirmed that such a mist causes various adverse effects on image quality and on the printing apparatus. The mist not reaching the print medium or the absorber scatters inside the apparatus, and contaminates various pieces of equipment by adhering thereto. For example, when a surface of the platen 206 shown in FIG. 1 or FIG. 2 is contaminated, the back side of the print medium 207 passing on the platen 206 is also contaminated. In this event, in a case where double-sided printing is executed for printing on front and back surfaces of the print medium, each printing surface itself is contaminated. Moreover, in a case where the apparatus includes an encoder for obtaining a current position of the print head 201, contamination of the encoder with the mist does not allow the encoder to accurately detect the position of the print head 201. As a result, printing positions of dots are shifted, and thereby the image quality is deteriorated.
In Japanese Patent Laid-Open No. 2002-086701, the mist in the margin-less printing is particularly seen as a problem. For the margin-less printing, the mist is reduced by controlling an amount of ink applied to the edge of the print medium. However, the margin-less printing is not the only factor which causes the mist. Even when the margin-less printing is not performed, generation of the mist may be seen as a problem. For recent ink jet printing apparatuses, there has been developed a technology of printing with a wide variety of ink by applying small ink droplets at a high frequency and with high density, in order to allow faster output of higher quality images. In such a situation, adverse effects of the mist are greatly concerned even when the margin-less printing is not performed.
However, the method described in Japanese Patent Laid-Open No. 2002-086701 only aims at the margin-less printing, and cannot sufficiently respond to the recently-observed adverse effects of the mist. Moreover, with a method of changing printing conditions only by confirming whether or not to perform the margin-less printing, the image quality is sometimes rather deteriorated than improved by reducing the application amount of ink more than necessary.